The present invention relates to bicycle pedal arm extensions and in particular to an apparatus which automatically extends the pedal arm during the downstroke and retracts each pedal arm for the upstroke while bicycling.
In riding bicycles the rider's legs push rotating pedals in a generally circular motion. The pushing is transformed into rotational torque which is transmitted to one of the wheels which in turn through frictional contact with the ground provides linear propulsion to the bicycle. Typically two pedals are positioned at 180.degree. with respect to each other on a solid rotating shaft which is supported with bearings through a portion of the lower frame of the bicycle so that pushing down on one of the pedals provides a corresponding lifting or raising of the other pedal. While competition cyclist both push and (with toe straps) pull the pedals as they ride, it has been found that the downward stroke is the most efficient and most forceful stroke for the typical bicycle rider. Even with experienced competition bicycle riders there is only a small force applied as the pedal is traversing upward from the bottom position back to the top position.
Since torque is a product of the force and length of the moment arm, it has been found that increasing the length of the bicycle pedal arms during the downward thrust can generate more torque with less force. Also, if the pedal arm is shortened during the upward stroke it will return more rapidly to the upward position and will again be ready for the powerful downward stroke.
Prior devices which have attempted to increase the length of the pedal arm during the downstroke have been complex, cumbersome, and subject to inefficiencies resulting from substantial amounts of sliding or rolling friction between offset cams and cam followers attached at both sides of the bicycle for interaction with extendible pedal arms.
In 1984, Chattin in U.S. Pat. No. 446,754 disclosed a telescoping pedal which is activated using a roller bearing in an offset cam plate. This concept was similarly disclosed in U.S. Pat. No. 4,519,271 also issued to Chattin in 1985.
In 1987, Xi in U.S. Pat. No. 4,706,566 disclosed another offset cam plate arrangement for providing varied pedal arm length.
In U.S. Pat. No. 4,807,491 issued Feb. 28, 1989, Stuckenbrok details various aspects and improvements to extension pedal arms. These arms are to be activated using an offset circular pattern using an offset cam plate similar to those of the preceding patents.
Another approach to pedal arm extension is shown in U.S. Pat. No. 4,882,945 issued to Trevizo Nov. 28, 1989 which discloses an apparatus which uses the relative rotation between the pedal held horizontal by the rider's foot and the pedal arm which rotates to provide a small amount of periodic extension and contraction of the pedal length.
Other substantially more complicated apparatus for changing the length of bicycle pedal arms have been variously described in U.S. Pat. No. 4,793,208 by J. P. Bregnard et al, and in U.S. Pat. No. 4,872,695 by T. Silvano et al.
None of the foregoing disclosures provide a completely adequate and efficient offset pedal extension apparatus.